1. Field of the Invention
The invention relates generally to methods for shattering earth formations by the detonation of explosives within boreholes formed in the earth formations. The invention specifically relates to inflatable devices used in the practice of the present methods for support of explosives and/or stemming within a borehole.
2. Description of the Prior Art
Various mining operations and earth removal operations are improved by a practice known as presplitting or shattering of earth formations in a controllable manner. As an example of a prior presplitting operation used in mining, a number of spaced boreholes are drilled in a formation which is to be shattered. Explosives are disposed within the boreholes and detonated to shatter the formation, thereby facilitating the removal of overburden to expose seams of material which is to be mined. Earth removal methods used for other purposes also have employed presplitting techniques. In operations of this nature, prior devices have been available in the art to "plug" boreholes drilled specifically for presplitting. Such devices have invariably been relatively expensive and relatively complicated in structure. Further, such prior devices are mechanically unable to support sufficient quantities of explosives and/or stemming necessary in presplitting boreholes of diameters approaching that of production boreholes. These prior devices are often incapable of adequately supporting explosives and/or stemming in even small diameter boreholes. Prior plugging devices employ structure such as plugged claws or the like which dig into a hole wall under the pressure surge of a blast. Other devices involve the mixing on site of foam generating reactive chemicals into an expandible rubber plug to achieve plugging of a hole. Similarly, wet drill holes ave been sealed with devices produced by DuPont (Australia) Ltd., these devices comprising two-layer polyethylene bags which contain two component polyurethane foam with the components packed separately as liquids in plastic bottles and sealed within the bags. Pressure applied to the liquid bottles within one of the DuPont bags causes lids to pop off of the bottles with a resulting mixture of the liquids, thereby forming polyurethane foam which hardens and causes the bag to expand against walls of the hole and to harden in place. Such devices as are described above are relatively expensive and require the handling of chemical materials. Further, after hardening of the foam materials within the device, the device cannot be subsequently reused or even repositioned or removed from the hole.
Temporary closure devices for boreholes have been provided by Fitzgibbon, Jr., in U.S. Pat. No. 3,357,193, these devices comprising inflatable, tubular structures which are inserted in a deflated condition into the upper end of a hole and inflated therein in order to temporarily close off the hole to prevent ingress of water, to prevent ice formation within the hole and to prevent blockage of the hole by undesirable material which can fall into an open hole. Further, the Fitzgibbon, Jr. devices prevent individuals from stepping into or falling into such holes with resulting injury.
However, the prior art has not provided an inexpensive borehole plugging device which can be either expendible or reusable according to the particular method of use. The invention provides for the first time such an inexpensive plugging device which can be rapidly and conveniently used in field blasting operations and which can be reused in many applications and even repositioned as desired within the borehole in the event that the plugging device is not initially positioned within the borehole in a satisfactory manner or in a desired location The relatively inexpensive nature of the present devices allows the practice of a variety of presplitting and blasting methods at a minimum of expense. The present devices and methods for their use thus constitute a significant and substantial advance in the art.